There is currently a problem in the nuclear field, and probably in other fields, where a leak at a tube in a nest of tubes where it is welded to a tube plate in a neat exchanger has to be made good without gaining access to the outside of the tube. The practice for dealing with this problem is to insert a length of repair tube into the leaking tube through the tube plate with one (the outer) end of repair tube explosively welded to the tube plate and the other (the inner) end brazed to the leaking tube.
We have now discovered that the quality of the braze can be affected by the presence of strain in the tube being repaired, such strain arising during the heating necessary to effect the braze. A predetermined tolerable level of said strain can be assessed by tests involving the brazing of specimens under various strains and then inspecting the brazes.